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Title: O 2 based resonantly ionized photoemission thermometry analysis of supersonic flows

Characterization of the thermal gradients within supersonic and hypersonic flows is essential for understanding transition, turbulence, and aerodynamic heating. Developments in novel, impactful non-intrusive techniques are key for enabling flow characterizations of sufficient detail that provide experimental validation datasets for computational simulations. In this work, Resonantly Ionized Photoemission Thermometry (RIPT) signals are directly imaged using an ICCD camera to realize the techniques 1D measurement capability for the first time. The direct imaging scheme presented for oxygen-based RIPT (O2RIPT) uses the previously established calibration data to direct excite various resonant rotational peaks within the S-branch of theC3Π, (v = 2) ← X3Σ(v = 0) absorption band of O2. The efficient ionization of O2liberates electrons that induce electron avalanche ionization of local N2molecules generating N2+, which primarily deexcites via photoemissions of the first negative band ofN2+(B2Σ<#comment/>u+−<#comment/>X2Σ<#comment/>g+). When sufficient lasing energy is used, the ionization region and subsequent photoemission signal is achieved along a 1D line thus, if directly imaged can allow for gas temperature assignments along said line; demonstrated here of up to five centimeters in length. The temperature gradients present within the ensuing shock train of a supersonic under expanded free jet serves as a basis of characterization more » for this new RIPT imaging scheme. The O2RIPT results are extensively compared and validated against well-known and established techniques (i.e., CARS and CFD). The direct imaging capability fully realizes the technique’s fundamental potential and is expected to be the standard of implementation going forward. The direct imaging capability can play instrumental roles in future scientific studies that rely upon acute characterization of thermal gradients within a medium that cannot be easily resolved by a point. Furthermore, the removal of the spectrometer greatly reduces the cost, complexity, and optical alignment associated with prior RIPT measurements.

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Publication Date:
Journal Name:
Optics Express
Page Range or eLocation-ID:
Article No. 40557
1094-4087; OPEXFF
Optical Society of America
Sponsoring Org:
National Science Foundation
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